Glass-fiber filter tubes have been employed for the filtration of gas or liquid streams, and typically have been composed of a plurality of interrelated, randomly disposed, glass fibers bonded into a self-supporting filter tube at the junction of the fiber crossover points by a variety of bonding agents. One class of bonding agents has been composed of inorganic material, such as silica sols. Another class of bonding agents comprises organic thermosetting-type resins. The filter tube is impregnated with the thermosetting or curable resin by immersing the dry filter tube into a solution containing the thermosetting resin, and, thereafter, heating the tube to drive off any volatile organic solvents and to effect the cross-linking or condensation of the organic resin. Thermosetting or cured resins employed as binders include phenol-formaldehyde resins, epoxy resins and silicone resins (see, for example, U.S. Pat. Nos. 3,767,054 and 3,972,694, both hereby incorporated by reference in their entirety).
Although such resin bonding agents are satisfactory for many purposes, filter tubes containing such resin binders often cannot be employed in certain applications, such as, for example, the filtration of halogen, such as liquid chlorine, or very strong mineral acid or highly oxidizing solutions. It is, therefore, desirable to provide an improved filter tube having a bonding agent which has substantially high chemical inertness.
In addition, it is also desirable to provide filter tubes of high and improved collapse strength and/or burst strength. The burst strength of glass-fiber filter tubes is improved by incorporating therein an integral, cooperative-bonded, open, reinforcing, scrim sheet material, such as an open-mesh, glass-fiber sheet. For Example, a helical coil of mesh material bonded within the walls of the filter tube improves the burst strength of a glass-fiber filter tube (see U.S. patent application Ser. No. 679,569, filed Apr. 23, 1976 (now U.S. Pat. No. 4,102,785, issued July 25, 1978), hereby incorporated by reference in its entirety). However, even improved and higher burst strengths of filter tubes than those described in the patent application, supra, are desirable, in order to avoid the necessity of employing separate external support screens (or internal support cores for improved collapse strength) at high fluid pressures, and for use of the filter tubes directly on compressed air lines at 100 to 125 psi or over.